Computerized Tomography or CT modality has been widely used for diagnosis and treatment follow-up purposes. It can provide very detailed anatomical structures of the human organs. For example, in oncology, CT is used to monitor therapeutic responses of a treatment to tumors by measuring size changes. However, it takes a long time, e.g., several weeks, for a treatment to be reflected in the size change of a tumor. SPECT (single photon emission computed tomography) is a modality that can provide immediate metabolic measurement of a human organ and/or tumors, allowing one to discriminate healthy tissue from diseased tissue at the functional level. While both CT and SPECT provide imaging information, the imaging obtained from SPECT cannot provide sufficiently detailed anatomical structural information about the human organs in the same manner that CT does. Furthermore, SPECT image resolution is much lower than CT, so accurate treatment planning may not be possible in SPECT images alone. Recently CT and SPECT have been combined into one imaging device, allowing both CT and SPECT images to be referenced across each other. Currently, the utilization of SPECT-CT imaging is utilized mostly at the image level. For example, SPECT and CT images may be overlaid on each other for cross-referencing. In percutaneous treatment of liver lesions for example, such as by Radio-Frequency Ablation (RFA) or chemoembolization, it is desirable to plan the treatment based on both the anatomical information and functional information. Furthermore, functional and anatomical images may be combined together for a more accurate segmentation of liver lesions.
It is therefore highly desirable to combine the anatomical information from CT for regional analysis with the functional analysis aspect of SPECT for a treatment planning and treatment monitoring at both the anatomical and functional levels.